EP0791877A1 - Electronic device providing a secure time reference for the protection of a program - Google Patents

Abstract

The electronic device, for verification of lawful use of a logic system is designed to be connected to a computer (11). The device includes a micro-controller (13) connected to a memory (14,15), an internal clock (16) and an internal battery (12). The micro-controller(13) uses an asymmetric crypto-graphic algorithm, which requires the use of a secret signature function and of a public verification function. The device contains the secret signature as well as the public verification function. The device can be connected to either the serial or parallel ports of a computer and is incorporated in a sealed casing. The device includes an interrogation counter (17) which is incremented for each interrogation of the device, it also includes a personalising counter (18) which permits the loading or reinstalling of user rights, in the form start dates and/or end of validity, of use duration. The algorithm is taken from amongst the following algorithms: RSA, FIAT- SHAMIR, DSA-DSS, GQ, EL-GAMAL.

Description

Technical area

The present invention relates to an electronic device delivering a secure time reference for the protection of software, this device being able to be connected to a computer.

State of the art

All computers, from the scientific calculator to the family model, have an internal clock and thus have a time reference. Many systems or software use such a time reference for different functionalities not related to their protection. Such a reference, in fact, is accessible and modifiable using the operating system of the computer concerned. It is therefore not a reliable reference.

Software piracy (illegal copies, use not in accordance with the user license, ...) is very common and constitutes significant damage for their publishers. Many protection methods have been used to date with varying degrees of effectiveness.

There are demo versions of software, in which some important functionality is not available, but there is no license to use software with all of its functionality for a limited time. Thus the rental or hire-purchase of software, does not exist, because there is no protection adapted to such concepts.

In general, it is very interesting to have a reliable time reference in order to be able to design new software or system protection mechanisms.

At present, the safest protections use hardware means associated with software, generically called "dongles" or "electronic keys". These hardware means are small external objects (boxes, floppy disks, etc.) which can be connected to computers, in particular by their serial or parallel ports. A dongle uses specific signals, and / or any other manufacturing "secret", allowing the software to ensure its presence during an execution and to accept an exchange of information.

• si le dongle envoie toujours les mêmes signaux, un faux dongle peut alors rejouer les signaux enregistrés en fonction de ceux émis par l'ordinateur ;
• si les signaux renvoyés par le dongle sont obtenus à partir de signaux émis par l'ordinateur comme résultat d'un calcul secret, alors le logiciel dispose du même secret dans son code pour vérifier l'authenticité des signaux transmis par le dongle ; par analyse du logiciel on peut alors retrouver ce secret pour réaliser ensuite un faux dongle.

Unfortunately, a device can be placed in the break between a computer and a dongle to analyze the signals exchanged. Also the use of a dongle has the following disadvantages:

• if the dongle always sends the same signals, a false dongle can then replay the recorded signals according to those emitted by the computer;
• if the signals returned by the dongle are obtained from signals sent by the computer as a result of a secret calculation, then the software has the same secret in its code to verify the authenticity of the signals transmitted by the dongle; by software analysis we can then find this secret to then make a false dongle.

The behavior of non-cryptographic dongles can thus be analyzed using a cut-off device or by analysis of the software code, to be reproduced subsequently, in the absence of dongles.

In all cases, the current dongles cannot provide time references, and therefore a fortiori reliable time references.

In addition, the custom dongles for a given software cannot be reused afterwards for another software.

Some distributed systems or software use a certified time reference for security functionality. Such a time reference is provided by a particular computer (or server), which authenticates with other computers requiring its service. But this computer can be "corrupted" by changing its internal clock, like that of any other computer. The other computers then trust it, but the time provided is inaccurate. Such operation used for internal security purposes in an organization is not suitable for software protection. Indeed it is then a question of protecting software of an organization against the illicit use of it by other organizations or individuals.

A computer providing a certified time reference (clock server) cannot be considered safe by a software publisher because this machine belongs to the user and not to the software publisher.

There are microprocessor cards that use an algorithm to allow authentication and certification. But these cards, which are not powered, cannot have an internal clock to deliver a certified time.

Thus, current devices do not allow a computer to have a secure time reference that can be used by software to combat piracy.

• de la satisfaction des conditions d'utilisation du logiciel ;
• de la présence du boîtier pour que le logiciel continue son exécution.

The object of the invention is to provide a secure time reference in a dongle, connecting for example to the serial or parallel ports of a computer, which software can interrogate to ensure:

• satisfaction of the conditions of use of the software;
• the presence of the box so that the software continues its execution.

Statement of the invention

The present invention relates to an electronic device for verifying the lawful use of software, capable of being connected to a computer, said device comprising a microcontroller connected to at least one memory, an internal clock and an internal battery, characterized in that that the microcontroller uses an asymmetric cryptographic algorithm, which is based on the use of a secret signature function and a public verification function, and in that said device contains the signature function secret, while the software contains the public verification function.

Advantageously, the device of the invention is incorporated in a sealed box.

Said device can include a query counter which is incremented on each interrogation of said device, and a customization counter which makes it possible to load and reset usage "rights", in the form of start and / or end dates. validity, duration of use, etc.

Advantageously, the algorithm is an asymmetric cryptographic algorithm taken from the following algorithms: RSA, FIAT-SHAMIR, DSA-DSS, GQ, EL-GAMAL.

Advantageously, the device of the invention makes it possible to limit the use of the software for a period of validity (three months of use from the first use for example), to limit the use of the software to a certain number of uses , and using an appropriate implementation of the software to limit its use to an approximate duration (about five hundred hours, for example).

The electronic device of the invention can be rechargeable and make it possible to buy back use time a posteriori on a simple telephone call.

The electronic device of the invention accepts post-personalization by certified orders, and is reusable

Brief description of the drawings

The figure illustrates the electronic device of the invention.

Detailed description of embodiments

the electronic device of the invention (10), as shown in FIG. 1, is able to be connected to the serial or parallel ports of a computer 11. It is supplied by an internal battery (12), and in particular contains a microcontroller (13), connected to memories, for example of the RAM (14) and ROM (15) type, and an internal clock (16).

This device can be incorporated in a sealed housing. Such an enclosure can, if it is opened, reset or destroy itself by any suitable physical means incorporated in it. Such a physical means known to those skilled in the art makes it possible to avoid the dissemination of secret information and incidentally makes any subsequent use of the software impossible.

The device of the invention is recognized by the software considered using a signature mechanism based on an asymmetric cryptographic algorithm, for example of the RSA (or Rivest-Shamir-Adelman), Fiat-Shamir, DSA-DSS type. , GQ (or Guillou-Quisquater), El Gamal, as described in numerous documents and in particular the work entitled "Applied Cryptography" by Bruce Scheiner (Edition John Wiley & Sons, 2nd edition, part III, chapters 19 to 21, pages 461 to 512, and part IV).

An asymmetric signature algorithm is based on the use of a secret signature function and a public verification function. Knowing one function does not allow knowing the other. The device contains the secret function, while the software to be protected contains the public service which only allows verification. The software to be protected therefore contains no secrets, because the knowledge of the public service does not allow signing messages.

All the interrogations of the device are carried out by the software, which sends it a random number to avoid replay, which consists for a foreign person of observing any transaction between two devices and executing this transaction again. When the device responds, the random number is returned along with the response to the query and the signing of the data. In the particular case of the RSA algorithm, the signature allows, by application of the public service, to reconstruct the data.

The observation of the exchanges between the computer and the device of the invention cannot be used by a foreign person because these exchanges are non-deterministic and cannot be replayed (presence of the hazard).

If we take the example of the RSA algorithm, S being the secret signature function, P the public verification function, has a random number, H the time (and the date), / indicating the operator concatenation, we at signature: c = S (H / a), and the public audit function P (c) = H / a.

When the device of the invention is questioned, it only responds if the planned methods are all satisfied (expiry date not reached, duration of use not reached, etc.).

• l'introduction du numéro de série du boîtier ;
• l'introduction de la fonction secrète asymétrique de l'éditeur ;
• la mise à l'heure de l'horloge ;
• l'initialisation du compteur d'interrogations (17) : celui-ci, qui est incrémenté à chaque interrogation du boîtier, permet de faire une correspondance entre le nombre d'utilisations du logiciel et une certaine durée d'utilisation du logiciel ; ce qui présuppose une implémentation appropriée du logiciel ;
• l'introduction de la date de début de validité, de la date de fin de validité, de la durée d'utilisation...

We will now consider the life cycle of a case; during manufacture, the software publisher performs:

• entering the serial number of the box;
• the introduction of the asymmetric secret function of the editor;
• setting the clock time;
• initialization of the interrogation counter (17): this, which is incremented on each interrogation of the box, makes it possible to make a correspondence between the number of uses of the software and a certain duration of use of the software; which presupposes an appropriate implementation of the software;
• the introduction of the date of beginning of validity, the date of end of validity, the duration of use ...

These data are no longer modified until a complete reset of the box (reuse). They will be called hereinafter "usage rights".

The personalization and post-personalization procedures are implemented before / during the sale (personalization) of the software and possibly in use (post-personalization) to update the data relating to the use of the software.

If the device of the invention is used as a certified clock without limitation of duration, particular values are assigned to the registers corresponding to the expiry date and the duration of use.

To carry out the exchange of information, the device of the invention accepts initialization / updating rights orders. These orders are certified by a standard procedure. Certificates are calculated by the software publisher using a symmetric algorithm and a secret key, which gives its power to assign rights to the publisher. This key is contained in said device and shared with the publisher. Each case has its own symmetrical key. The editor is able to find all these keys by a conventional process of diversification of a mother key from the serial number of the box.

A personalization file contains the rights and their certificate. It is delivered to the user when purchasing the software or updating rights. This file does not contain any secret information.

Such an operation allows absolute rights management (date, number of uses). To manage these elements incrementally (add 100 uses for example) you must protect yourself against the replay of post-personalization. For this purpose, the device has a personalization counter (18).

Initialized at 0, this counter is taken into account in the calculation of certificates. The box accepts the update of rights if the transmitted value is strictly greater than the current value. The transmitted value is then assigned to the counter.

The total reset of the case, which allows its reusability, does not need to be certified.

Claims (6)

Electronic device for verifying the lawful use of software, suitable for being connected to a computer (11), said device comprising a microcontroller (13) connected to at least one memory (14, 15), an internal clock (16 ) and an internal battery (12), characterized in that the microcontroller uses an asymmetric cryptographic algorithm, which is based on the use of a secret signature function and a public verification function, and in that said device contains the secret signature function, while the software contains the public verification function. Device according to claim 1, characterized in that said device is connected to said computer by its serial or parallel ports. Device according to claim 1, characterized in that it is incorporated in a sealed housing. Device according to claim 1, characterized in that it comprises an interrogation counter (17) which is incremented on each interrogation of said device. Device according to claim 1, characterized in that it comprises a personalization counter (18) which makes it possible to load and reset "rights" of use, in the form of start and / or end dates of validity, duration of use. Device according to claim 1, characterized in that the algorithm is an asymmetric cryptographic algorithm chosen from the following algorithms: RSA, FIAT-SHAMIR, DSA-DSS, GQ, EL-GAMAL.

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